Washington — The US Supreme Court on Tuesday cast a skeptical eye toward a ground-breaking environmental case that seeks to use public nuisance law as a way to force five major power companies to reduce their emissions of greenhouse gases in the fight against global warming.

In questions from the bench during an extended 80-minute oral argument session, many of the justices expressed concern about using the judiciary to by-pass the approach to greenhouse gases embraced by the Environmental Protection Agency (EPA) and Congress.

Chief Justice John Roberts said litigation against major power companies over global warming raises a wide variety of policy issues, including questions about the potential cost to the US and world economies.

“The whole problem of dealing with global warming is that there are costs and benefits on both sides, and you have to determine how much you want to readjust the world economy to address global warming,” Chief Justice Roberts said. “I think that’s a pretty big burden to impose on a district court judge.”

Rather than waiting for the EPA to issue regulations and begin enforcing them, a coalition of six states and New York City took matters into their own hands. They accused the five power companies of being among the largest greenhouse-gas polluters in the country – contributing to a public nuisance through the emission of 650 million tons of carbon dioxide a year. The states asked a federal judge to order the companies to cap their emissions and develop a plan to systematically reduce their contribution to greenhouse gases.

The issue at the high court is whether the lawsuit should be dismissed or allowed to proceed to trial.

New York Solicitor General Barbara Underwood, representing the suing states, said the greenhouse-gas case could be handled the same way judges have long resolved suits involving public nuisances. The judge establishes facts at a trial, takes testimony from experts, and determines a reasonable remedy, she said.

Justice Ruth Bader Ginsburg said the suit sought to establish a federal trial judge “as a kind of super EPA.” Asking a judge to cap and monitor plant emissions “sounds like the kind of thing that EPA does,” she said.

Several justices noted that the EPA has begun regulating emissions of greenhouse gases. The agency has authority under the Clean Air Act and has opted to proceed on an incremental basis, focusing first on certain motor vehicles and pledging to regulate fixed sources of carbon dioxide, such as power plants, next year.

“Something that is imminent may never happen,” Underwood said. “The case is here now, and there is no federal statute or regulation that currently regulates the emission of greenhouse gases by existing, unmodified power plants.”

How would a district judge deal with the tradeoffs? asked Justice Samuel Alito. A decision capping emissions might involve increased costs of electricity, cause jobs to be lost in a region, and perhaps deprive some residents of the ability to pay for air conditioning in the summer. How would a judge decide what is reasonable? he asked.

“We’ve alleged that this can be done without increasing the cost to consumers,” Underwood said. “That may seem … that …,” she paused, searching for the right word.

“ ‘Implausible’ is the word you are looking for,” Justice Antonin Scalia interjected. The courtroom erupted in laughter.

Justice Stephen Breyer asked Underwood whether a federal judge has the authority to impose a tax on the discharge of excessive levels of carbon dioxide.

“I don’t think so,” Underwood replied.

So how does the judge have the authority to order a reduction in emissions when that reduction will likely cause an increase in the price of electricity? Justice Breyer asked.

“It is up to the defendant to decide how to do it,” she said.

Peter Keisler, representing the power companies, told the court that there is a reason global warming is a contentious, difficult issue in international negotiations, at the EPA, and in the halls of Congress. It requires policymakers to make difficult choices to balance environmental risks and benefits against economic benefits and costs for remedies that could be transformative.

“The problem with courts attempting to replicate what is going on in those venues is not simply that the matter is complex,” he said, “but there is no legal principle here to guide [a judge’s] decision.”

He urged the court to dismiss the case.

US Acting Solicitor General Neal Katyal also argued that the case should be dismissed. “This court has never had a case of this scale and scope,” he said. “When a problem is of this magnitude, everyone is a potential polluter, everyone is a potential victim.”